Linux Kernel 2.4 Ascends The Big Iron

Find out how the new Linux kernel 2.4 increasingly supports higher-end machines, such as the IBM S/390 Mainframe, and Beowulf clusters in this latest kernel month article.

The new Linux kernel 2.4 increasingly supports higher-end machines,
such as the IBM S/390 Mainframe, and clusters. 2.4 also better
supports many of the peripherals associated with this class of
machine, like gigabit Ethernet, fast-switching,
multi-device support for RAID and LVM, improved SCSI drivers, and more.

IBM, as part of its pledge to greater serve Linux with support,
software, and services has several mainframe class machines available
from the factory with Linux installed. The IBM S/390 has received
the most attention from the Linux community, after it was announced that
David Boyes at Dimension Enterprises had run 41,400 separate
instances of Linux simultaneously on one mainframe machine
before it ran out of resources.

David Boyes said, "The test succeeded in demonstrating the
capacity of Linux for S/390 for a telco that was considering
the purchase of 25 Sun servers to provide ISP and ASP services.
Dimension worked with the telco to consolidate its distributed Internet news
service onto the S/390. The initial phase included 250 production
Linux servers running on a single S/390. Later, it was expanded to
650 production Linux servers on a single S/390 server."

The S/390 has an interesting feature where a guest operating system
can be loaded into a Virtual Machine (VM). So what good is this?
Picture the needs of a web hosting company, their higher end
customers demand a dedicated machine running Linux. This way, the
customer has full root access, and can install and remove software as
they see fit. They need not worry about other customers
messing with thier configurations.

This is ideal for the customer, but can create problems for the web
hosting company. As their customer base grows, they will run out
of space in their colocation facility. Even with rack-sized systems, it
won't take long before there isn't enough room for more dedicated
customers.

Instead, if this same web hosting company were to buy a
mainframe about the size of a refrigerator, they could partition the
machine into several thousand separate Linux instances. Each instance
is dedicated to one customer, who would have root access to that
instance. Because of the partitioning between instances, all of the
virtual machines can't interfere with each another.

It is also an advantage for the web hosting company, because dedicated
mainframe hardware has always been designed with high availability
and reliability in mind. Often, they are many times more stable than
commodity PC hardware. The price ratio is also favorable even with
commodity hardware, several thousand dedicated boxes add up quickly.

Mainframes, often thought to be dinosaurs by newer generations, seem
to be making a Jurassic Park comeback. Once highly
proprietary, mainframes are now adopting open standards like
TCP/IP, gigabit Ethernet and Linux.

In kernel 2.4.1 the /usr/src/linux/arch/s390 directory contains the
following s390 architecture specific files:

With only half a meg worth of code, the kernel can support this
mainframe. It is amazing that the majority of the same code which
runs on a mainframe also executes on your home PC. This unified code
base benefits both mainframe and home users.

Another important big iron feature with 2.4 support is clustering. In
the Linux world, most users quickly hear of the fabled Beowulf. No,
not the epic poem, but an open source clustering software solution,
originally developed by NASA's Goddard Space Flight Center.

From the history of Beowulf:
"In the summer of 1994 Thomas Sterling and Don Becker,
working at CESDIS under the sponsorship of the ESS project,
built a cluster computer consisting of 16 DX4 processors connected by
channel bonded Ethernet. They called their machine Beowulf. The
machine was an instant success and their idea of providing COTS
(Commodity off the shelf) base systems to satisfy specific
computational requirements quickly spread through NASA and into
the academic and research communities."

As commodity Intel hardware become both faster, and cheaper, it was
almost natural to connect together off the shelf PC's into clusters.
Linux, being open source and easily modified was also ideal for this
purpose. In fact, some of the faster super-computers in the world
run Linux Beowulf clusters.

One thing Beowulf needs more than anything else is fast
interconnections. Unless a parallel program is "embarrassingly
parallel", each of the nodes has to talk to one another to transmit
and receive data. With a slow network, fast CPUs end up stalling
while communication is taking place, slowing down overall computation.
Kernel 2.4 continues to and improves its support devices like
gigabit Ethernet, and other advanced networking solutions to help
alliviate communications problems.

2.4 continues to builds on Linux's excellent 64-bit support,
in the process making Linux the
first out the door with IA64 (Itanium) support. Linux also
has excellent Alpha support, which many Beowulf clusters have
used to great effect. Portions of Titanic were rendered using
a Linux Alpha Beowulf cluster. Many scientific labs also use
Alpha Cluster for complex models, like weather simulations.

With growing support for mainframes, Linux will continue to find its
way into new and interesting niches. Someone trained in Linux in
college, may very well find themselves with a job working with
mainframes, with very little re-training required. Linux is
quickly become the UNIX, running on everything from a hand-held
device all the way to a mainframe. Tune in next week to find out
how the same 2.4 kernel runs on embedded devices and PDAs.